CIHM 

ICI\/IH 

Microfiche 

Collection  de 

Series 

microfiches 

(l\/lonographs) 

(monographies) 

i 

C.n.d'1..  InttituM  for  Historical  Microroproductlom  /  Institut  Canadian  da  microraproduction*  historiquas 


996 


Technical  and  Bibliographic  Notes  /  Notes  technique  et  bibliographiques 


The  Institute  tias  attempted  to  obtain  the  best  original 
copy  available  for  filming.  Features  of  this  copy  which 
may  be  bibliographically  unique,  which  may  alter  any  of 
the  images  in  the  reproduction,  or  which  may 
significantly  change  the  usual  method  of  filming  are 
checked  below. 


El 


D 


D 


Coloured  covers  / 
Couverture  de  couleur 


j     j      Covers  damaged  / 

' — '      Couverture  endommagee 

I     I      Covers  restored  an*or  laminated/ 
Couverture  restauree  et/ou  pelliculee 

I     I     Cover  title  missing /Letitrede  couverture  manque 

I     I      Coloured  maps  /  Cartes  geographlques  en  couleur 

r~|      Coloured  ink  (i.e.  ottierttian  blue  or  black)/ 
Encre  de  couleur  (i.e.  autre  que  bleue  ou  noire) 

I     I      Coloured  plates  and/or  illustratkxis  / 
— '      Planches  et/ou  illustrations  en  couleur 

I     I      Bound  with  other  material  / 

Relie  avec  d'autres  documents 


Only  edition  available  / 
Seule  edition  disponible 

Tight  binding  may  cause  shadows  or  distortion 
along  interior  margin  /  La  reliure  serr^e  peut 
causer  de  I'ombre  ou  de  la  distorslon  le  long  de 
la  marge  interieure. 

Blank  leaves  added  during  restorations  may  appear 
within  the  text.  Whenever  possible,  these  have 
been  omitted  from  filming  /  II  se  peut  que  certaines 
pages  blanches  ajoutees  lors  d'une  restauration 
appaiaissent  dans  le  texte,  mais,  knsque  cela  eiait 
p<»sifale,  ces  pages  n'ont  pas  Hi  flmees. 


L'Institut  a  microfilm*  le  meilleur  examplaire  qu'il  lui  a 
Me  possible  de  se  procurer  Les  details  de  cet  exem- 
plaire  qui  sont  peut-Stre  uniques  du  point  de  vue  bibli- 
ographique,  qui  peuvent  modifier  une  image  reproduile, 
ou  qui  peuvent  exiger  une  modifications  dans  la  mSth- 
ode  nomiale  de  filmage  sont  indiqufe  ci-dessous. 

I     I     Coloured  pages/ Pages  de  couleur 
I     I     Pages  damaged  /  Pages  endommagies 


D 


Pages  restored  and/or  laminated  / 
Pages  restaurees  et/ou  pellicuiees 


r^      Pages  discoloured,  stained  or  foxed  / 
— '      Pages  decolorSes,  tachetees  ou  piquees 

[^     Pages  detached/ Pages  dStachSes 

n7     Showlhrough/ Transparence 

I     I     Quality  of  print  varies  / 

' — '      Qualite  inigale  de  I'impression 

r~|      Includes  supplementary  material  / 

Comprend  du  materiel  supplimentaire 

I  I  Pages  wholly  or  partially  obscured  by  errata 
— '  slips,  tissues,  etc.,  have  been  returned  to 
ensure  the  best  possible  Image  /  Les  pages 
totalement  ou  partiellement  obscurcies  par  un 
feuillet  d'errata,  une  pelure,  etc.,  ont  6t6  filmees 
a  nouveau  de  fa9on  i  obtenir  la  meilleure 
image  possible. 

I  I  Opposing  pages  with  varying  colouration  or 
— '  discolourations  are  filmed  twice  to  ensure  the 
best  possible  Image  /  Les  pages  s'opposant 
ayant  des  colorations  variables  ou  des  decol- 
orations sont  filmees  deux  fois  afin  d'obtenir  la 
meilleur  image  possible. 


n 


Additional  comments/ 
Commentaires  suppiementaiies: 


Thii  ittm  is  fitmad  at  tti«  riduction  ratio  chackad  balow/ 

Ce  documant  ast  film*  >u  taux  de  riduetion  indiqu^  ci-dattoin . 

lOX  14X  18X 


2X 


2SX 


30X 


12X 


The  eopv  fllnwd  har*  hai  b««n  raproduead  thanks 
to  tha  ganarotltv  of: 

Blsckar-Nood  Library  of  Biology 
McCm  Unlverilty,  Montrool 


L'axamplaira  fllm4  ful  raproduit  griea  *  It 
04n4roilti  da: 

Blacker-Wood  Library  of  Biology 
NcCtll  Unlvaralty,  Montreal 


Tha  imagaa  tppaaring  hara  ara  Iha  baat  quality 
poatlbla  considaring  tha  condition  and  tagibility 
of  tha  original  copy  and  In  kaaplng  with  tha 
filming  contract  apaclficatlona. 


Lat  Imagat  lulvsntas  ont  M  raprodultai  avac  la 
plus  grand  toln,  compta  tanu  da  la  condition  at 
da  la  nattata  da  raxamplaira  filmi.  at  an 
conformM  avac  lai  conditions  du  eontrat  da 
fllmaga. 


Original  copies  in  printod  papar  eevars  ara  fllmad 
baglnning  with  tha  front  covar  and  andlng  on 
tha  last  paga  with  a  printad  or  illustrstad  impraa- 
slon,  or  tha  back  covar  whan  appropriata.  All 
othar  original  copias  ara  fllmad  baglnning  on  tha 
firat  paga  with  a  printad  or  illustratad  Impraa- 
sion.  and  andlng  on  tha  last  paga  with  a  printad 
or  illuatratad  Impraasion. 


Las  axamplalras  orlglnaux  dont  ia  couvartura  an 
paplar  ast  Imprimts  sont  filmte  an  commangant 
par  la  pramiar  plat  at  an  tarminant  aoit  psr  la 
darnltra  paga  qui  comporta  una  ampralnta 
d'Imprasslon  ou  d'illustratlon,  soit  par  la  lacond 
plat,  aalon  la  eas.  Tous  las  autras  axamplairas 
origlnaux  sont  fllmto  an  common9ant  par  la 
pramlira  paga  qui  comporta  una  amprainta 
d'Imprasslon  ou  d'illustratlon  at  an  tarminant  par 
la  darniira  paga  qui  comporta  una  talia 
amprainta. 


Tha  laat  racordad  frama  on  aach  microficha 
shall  eonuin  tha  symbol  —^  (moaning  "CON- 
TINUED"), or  tha  symbol  7  Imaaning  "END"), 
whichavar  applias. 


Un  das  symbolas  suivants  spparaltra  sur  Is 
darnitra  Imaga  da  chaqua  microficha,  salon  la 
cas:  la  symbols  —^  signlfia  "A  SUIVRE ',  la 
symboia  V  signlfia  "FIN". 


Mapa,  platas,  charts,  ate.,  may  ba  fllmad  at 
diffarant  raduction  ratios.  Thosa  too  larga  to  ba 
antlraiy  includad  in  ona  axposura  ara  filmad 
baglnning  in  tha  uppar  laft  hand  eomar,  iaft  to 
right  and  top  to  bottom,  as  many  framas  as 
raqulrad.  Tha  following  diagrams  lllustrata  tha 
mathod: 


Laa  cartas,  pianchas,  tablaaux,  ate.  pauvant  itrs 
fllmta  A  das  taux  da  rMuction  dlfftrants. 
Lorsqua  ia  documant  ast  trap  grand  pour  ttra 
raproduit  »n  un  saul  cliche,  II  ast  film*  t  partir 
da  I'angla  auptriaur  gaucha,  da  gauchs  1  droits, 
at  da  haut  an  bas,  an  pranant  la  nombra 
d'Imagas  nAcsssaira.  Las  diagrammas  suivsnts 
iilustrant  la  mtthoda. 


1 

2 

3 

1 

2 

3 

4 

5 

6 

MKtOCOW    RISOIUTION   TUT   CHAIT 

(ANSI  and  ISO  TEST  CHART  No.  2) 


1.0 

la  ^    ^m 

m 

III 

1 

I.I 

,.25  1 

J     -APPLIED  IIVt4GE     In, 


.*> 


tl!.  rvS'Y  WOOD. 

S  WMlTtH«LL  COUHT, 

l-ONUON.  S.W.I, 


Co«vY.\.'\.'Cft,C'ft,X»  o^ 


The  Eyelids  and  Lachrymal  Apparatus  of  Birds 


DR.  CASEY  A.  WOOD, 
Chicago,  III. 


(REPBINTED   FROM   OPHTHALMOLOOT,    JULT,    Itlt) 


THE  EYELIDS  AND  LACHPYMAL  APPAHATCS  OF 

BIRDS. 

Caut  a.  Wood,  U.  D,, 

OBICAOO. 

Illuitratid. 

The  amngement  by  which  the  iDterior  surface  of  the  eyclHill  ci 
Birda  i>  cleanaed  and  uthenriae  protected  from  rarioua  forma  of 
Injury  difftra  matarially  from  that  vhich  one  flnda  in  other  Terta- 
bntaa.  Eren  ttr  thoae  who  are  not  ipaciaUy  intareated  in  compan- 
tire  anatomy  and  phyaiology  it  often  many  pointa  of  contact  with 
hnman  ophthalmology,  and  thia  ia  the  writar*!  chief  axcuae  for  thia 
artiela.  Moat  of  the  inreatigationa  that  form  the  baaia  of  thia  paper 
ware  made  in  the  phyaiologioal  laboratoriea  of  Stanford  tTnivera- 
ity,  ia  coojonction  eapacially  with  Profeeaor  Slonakar.  The  raaolta 
of  theie  letearchea  ware  Srat  reported  to  the  Ophthahnological  Con- 
gieaa  at  Oxford  in  July,  1914,  and  publiahed  in  the  Americm  En- 
cueleptil*  vf  Opkthatmohgj/,  to  whsae  pobliaber  the  writer  ia  in- 
dabtad  for  the  iUnatrattoaa. 

That  one  may  appndate  the  part  pkyed  by  the  eyelids  and  the 
lachrymal  apparatna  in  the  vlaion  of  birda  it  ia  eaaential  not  only 
that  the  aecretion  and  lamovat  of  the  tear*  ahoold  be  atndied  but 
that  the  diapoaition  of  thr  bulbar  and  palpebral  mnaclea  ahonld  be 
borne  in  mind. 

The  tfU§niu4  oovaring  the  avian  ayaKiit  is  more  homy  than  in 
man.   It  ia  attached  to  tha  «or:  ai  by  dalioata  flbrea. 

The  (ami  plait  of  the  letaar  tU  ia  compoaed  of  cloaely  packed 
conaectiTe-tiaaaa  ilbrea,  in  which  one  occaaionally  Unda  ipindle- 
ahaped  or  round  cellt ;  but  none  of  these  can  properly  be  described 
aa  cartilage  calla.  A  dalieate  network  of  reaaela  snmnn  i  the  tar- 
sal plate. 

In  some  birds  a  fatty  layer,  more  or  lees  marked,  is  found  in  a 
well-defined  space  between  the  lid  edge  and  the  upper  margin  of 
the  tarsus. 

The  occompanying  illuatration  shows  the  lid  margint  of  the 
Sparrow  to  be  compoaed  of  about  34  (17  in  each  lid)  deeply  pig- 

(RBPRIIfTBD  ntOK  OPHTHALHOLOOT.   JTJX.T,    ItlS) 


«  t'M«y  A.  Wood, 

nicntiKl,  irregular.  Muugc-likii,  wgmnnU.  They  are  offen  ileeplv 
indcnW  about  lliiir  middle,  thui  preacnting  a  picture  entirely 
unlike  the  I  '  edgea  of  man. 

These  legmonta  undergo,  during  life,  apparent  djangea  in  tiic 
and  shape,  probably  aa  the  reanlt  of  winking,  partial  or  complete. 
Close  inspection  u{  them  shows  that  some  of  the?u  segmenu  are 


^^^'"MjfiAii'  '','??„55''.id%i:rkrrr"'  °' ""  "••"■"■ """' '"  "•'  ""■ 

crossed  by  indentations  which  may  become  entirely  smooth  again ; 
other  parts,  smooth  and  rounded  a  moment  before,,  may  present  a 
creased  or  divided  appearance,  so  that  photographs  or  drawings  of 
'-''5  "I'i'lipJPi"™*'  «'->'?--''"D'i.'ig-fe8ult«  ao.fsr,  aa  the  mai-giu.i 
of  the  lids  are  concerned.  In  Passer,  as  i'  most  birds,  there  is  no 
well  defined  intermarginal  apace.  A  feather  (eyelash)  is  geuerallv 
placed  below  each  palpcbr^!  segment,  but  the  former  may  bi;  misi- 


Kfirftth  and  Lavhrifmal .\ ppanttit*  of  Hirdu, 


\ng  »\  the  outer  and  innor  cin'l.i,  while  otmr  tu(ta  ii    avallin-l 
over  the  lid  lur/iice. 

The  inttrjat  tbml  ipace  viriei  koinewhat  in  the  itptrrow :  [kt- 
hapii  it  is  a  litue  mure  circular  and  smaller  whi'n  tho  bini  wH'om- 
moilut"-  ':r  near  viiion.  'ITie  acconipunyinK  illuatralinn  jjivM  .in 
idea  of  thu  average  relative  tizc  of  the  pupil  and  of  the  inlerspai'i! 
during  fixation  for  a  near  object. 

It  will  alio  be  noticed  that  thia  ipaco  ia  entirely  filli'il  ,iy  ihi' 
Sparrow's  cornea,  a  condition  i;ntirely  unlike  tliat  in  mammala. 

The  space  is  8.9  mm.  wide  and  4.5  mm.  long.  There  is  no 
lachrymal  caruncle  or  anything  to  indirate  it,  nor  would  one  exixvt 
it  if  the  higher  vertebrate  caruncle  be  a  veatigiary  remains  of  tlii. 
n.  titating  membrane. 

In  the  great  majority  of  birds  we,  for  obvious  reasons,  do  not 
speak  of  an  internal  and  external  canthus  but  of  anterior  and 
potterior  canthi. 

In  Sparrow-like  birde  the  pigment  of  the  rounded,  dark  brown 
lid  border  does  not  extend  beyond  the  point  where  it  touches  the 
ryeball,  nor  does  it  more  than  reach  the  nalpebral  derma.  There  is 
more  pigment  in  the  upper  lid  than  in  the  lower.  When  closed, 
the  junction  of  the  two  lids  is  well  above  the  pupil,  so  that  the 
cornea  is  fully  pro.ected.  Probably  there  is  no  upward  rotation  of 
the  eyeball  in  sleep.  The  lower  lid  follows  the  usuel  law  in  biriN, 
of  being  the  movable  one. 

As  a  general  proposition  it  may  be  stated  that  in  resiwct  of  sizi'. 
motility,  etc.,  the  lids  in  the  Bird  and  Man  are  reversed,  viz.,  the 
lower  lid  is  the  more  important  in  Birds;  the  upp^r  lid  in  human 
beings.  The  naked  condition  of  both  avian  eyelids  is  not  seen  when 
the  eye  is  ipen  because  the.,  are  then  obscured  by  tlie  surrounding 
feathers.  The  external  surface  oi  each  lid  is  quite  thin,  smooth, 
whitish-blue  end  devoid  of  feathers,  except  for  a  few  solitary  shafts. 

Very  li!  y  there  is  no  interference  with  the  luminous  sense  and 
light-direction  sense  when  the  Bird's  eye  is  closed. 

There  is  no  differentiated  tanue  in  the  upper  lid,  which  is  much 
shorter  and  thicker  than  the  lower  one,  although  the  ronvoluted 
cylindrical  margin  of  the  upper  lid  is  better  shown  in  the  upper 
than  in  the  lower  lid. 

Unlike  Man  and  many  other  mammals,  there  is  no  true  union  of 
the  conjunctivae  of  the  two  lida  before  the  bird  is  bom.  In  the 
Sparrow  (probably  in     1  the  Passeriformes)  the  lids  are  wide  open 


I 


♦  Cauf  .1.    Waa.: 

evidence  Ui.t  „y  oigwiio  union  occur,  betwwm  the  lid  m.r«in.  in 
h«,  ..born-blind"  bird.  In  .„  probubility  U..  cl„«d  e^ZZ 
to  tonic  contr«tion  of  the  orbicul.ri.  u  ,  Jlght  reSe,  „t 

;,I  "T't'  "'  '*'  •*""•  *"  ""  o^<"''<^  palpebrarum,  the 
>'<^orpalpel,ra.  „p.Won.,  .nd  the  d.pr^„  ^'^fr^  inMorU 
A«ording  .0  Leuck.rt  (Ora.f^Sa«n»ch  HandiJk  d.  g,.  Aug^. 
hnlkunJe,  Vol.  II,  1876,  p.  US)  ,„d  Doenecke,  they  .re  ,11  .tri'ted 

Zt^         i^'Z"-  ■'  P-  "»>  *«"««»  **«  orbicuUri.  to  be  , 

(M  one  might  expect  from  the  f«t  th.t  the  l.t.er  i.  more  mobll. 
U,.n   he  upper    .nd  Utter  developed  than  the  levator  of  the  uppe 

lnlT^«  'IJ^*?.""™"^  "'"  ""  ""«""  ■•"'•"  <"  the  lid  pUto 
."  ioint^  .11  ••  •''"°"l"'«  '"  Ziet»chm.nn  both  muKle. 
J„™^  ™!?  V  "'"*"  '"  ""  "^P""  "'  ">»  o"-'*.  where  they 

form  p.rt  of  .  common  muicl.  mu.;  .Ithough  Slon.ker  h..  not 
b«n  .ble  to  verify  thi.  finding.     81on,ker,  however.  ag««  Uh 
Z.e.^hm«,n  th.t  the  orbicuLri.  i.  ,  .mooth  m„«i;,^.  ^  ' 
the  depreewr  .nd  levator  p.lpeb™i  are  .triated. 
thirH  °7'7™"",«  '^"'  ""o  Sparrow  tlie  writer  found  that  the 

the  bird.  eye.  The  paire.  U,.  .lo«  very  .lowly,  if  at  ^I  under 
the  .  imulanU  u«d.    The  phyi.ological  e/periment.  bear  out  wh! 

IHZ^T""'"'-  '"■'  '■'"'  ""'  "'"™""*'  "  --""ot 

„,«?iL°''*'"l'''~  "  "'  "'"°"'^  **"  "»•«'«  i"  th"  Sparrow  a. 
may  be  «en  by  examining  the  «x«mp«,ving  flg„„.  u  ^pe„  ° 
mere  hno.  on  horizontal  .ection,  and  ^'Jn  ToU  in  eS  L^ 
t.on,.  It  ,.  attached  to  the  .kin  and  doe.  not,  a.  in  Man  nprL 
out  and  mingle  it,  fib,«  with  neighboring  for,.h.ad.  ta^uMofTh 
lower  hd)  and  lachrymal  apparatus  muscle.  ' 

Jffird'lVrV'^J"^  "  ""  ""•"  ™"'''  -"»«""•  -">■  «■«•''>«••'  i" 
tnc  Bird  8  hd  of  the  human  muscle  of  Eiolan. 

.Mthough  tteie  i.  every  reason  to  believe  that  the  non-striated  or- 
bicularis of  Pa,>,er  domesticm  is  supplied  by  fibre,  deri™-  * 

■di    "'„'!"'•  "r^— '™«»g  the  cou^  of'theTb,; 
and  d,^.™n,ng  their  origin,  has  not  yet  been  solved. 
In  the  Hen  the  ciliary  f„tKer,,  or  eyelashe,,    mom  nearly  re- 


-n...  •  thi.k,    .^,^  |„i„,  ,„,,  ,hi,  ,„„,,„,,|„„,„  „  ,.,,^,h^,„ 

I.  .11  Ih..  in,.™  pron„un«,l  in  th.t  th,.«^^  IHirom,  f,.„ih..n.  ,„•  in. 

point.  intiTl.,,,  with  thi.  I..I,,..  I  f,.„,i  ,,„.,  , ,  ,;  f 

Mo„K.vor,  wh«„  ,h„  lid.  .,„  el,*.,!  U,„  inrnT  li.l-.n.rlL  roll     i 
"...r.  than  ,.  U»  ™.,      „l,  ,l,„  S,«„„w.  „,  tl„t  ..,..  i„l™«  '    '" 

rh:ri:Mr'"^-'-"- ""•"'""•  ""•'^- '"-" 

TlH«  f..thor.t..vel«he.  belong  to  th.-  .l.,,.  „f   ,i|„,,|,„ „. 

th«...l  f.  ..her.  With  no  true  v.ne.,  thirty  to  .hi.tv-Hv..  !,1  Z  J, 


•nd  «l;„.'i:;r'',""""'  ■•■>■•■  "  ""■  African  u.,rlch_s,ru,hl„  o.mel,,..   ,w,„d 

more  being  found  in  the  upp..^  lid  ,h.n  in  the  lower.     Of  „„mv 
ob«rv.  ,„n,  the  writer  found  the  average  p,.^,r,i„„  ,„  ,„  ,,  T 
In  n,„«t  ,n8t«nce,  the  plumule  of  the  ,uft  rine.  ju.t  «l«ve  the  J,rt 
n..rg,n  o,  .he  eyelid  and  i,  bent  or  direeted  awav  fr„,„  the  1,  er  L 

two  eanth,.     The  plumules  do  not  n,«.t  or  fom,  a  gcnen  over  th.. 

Z^Z         T", '"'''"'"'"'  ""  '""'  »"•  «"""''>■  wanting  or  a„. 
in^rted  irregularly  „me  di.Unee  /r«m  the  margin  „f  L  li^ 


•  C(u$p  A.  Wood. 

At  the  inner  ciintbus  and  especially  on  the  lower  lid  the  cUiary 
tufts  are  (to  the  number  of  5  or  6)  directed  straight  forward. 

Scattered  over  the  two  otherwiie  naked  lids  a  varying  number- 
usually  half  a  dozen-flf  plumules  can  generally  be  seen  of  the 
same  size  as  those  at  the  lid  margins.  Sometimes,  though  rarely 
they  form  a  regular  second  row  of  cilia  along  the  margin  of  the  lid.' 

The  eyelashes  of  Sparrow-like  birds  do  not,  judging  from  their 
position  relative  to  the  lid  margins,  act  as  a  protection  to  the  eye 
An  examination  of  them  shows  they  are  not  prominent  enough  for 
this  purpose;  they  are  too  far  removed  from  the  interpalpebral 
space;  they  do  not  overhang  the  lid  margin,  and  they  do  not  intei- 
to^k  when  the  eye  is  closed,  as  in  many  of  the  other  vertebrates 
They  appear  in  bird  life  to  occupy  a  place  intermediate  between 
the  Ostrich,  Seriema,  and  other  birds  that  possess  well-developed 
and  useful  eye  protectors,  and  the  Parrots  that  have  none  at  all. 

Nevertheless  the  cilia  of  the  Sparrow  are  more  developed  than 
in  some  other  Birds,  though  less  so  than  in  the  Ostrich,  Sc.  ..ma  and 
the  Birds  of  Prey. 

The  eyelashes  of  most  Birds  do  not  lake  much  if  any  part  in  the 
protection  of  the  eyeball  during  sleep  or  on  other  occasions.  The 
Sparrow  does  not  entirely  close  his  paited  lids  unless  the  cornea  is 
touched  with  some  blunt  object,  as  a  dissecting  needle,  although 
any  approach  of  the  object  increases  markedly  the  contractions  of 
the  nictitating  muscles. 

Except  during  sleep,  or  in  particular  emergencies,  the  paired  lids 
of  Birds  are  rarely  closed.  Most  of  the  ordinary  functions  of  the 
human  lid  are  performed  by  the  nictitating  membrane.  The  true 
lids  of  the  Sparrow  may  indeed  be  regarded  as  accessary  organs 
whose  functions  are  confined  to  the  protection  and  moistening  of 
the  bird  s  eye  only  while  he  sleeps.  The  writer  and  Slonaker  have 
not  been  able  to  observe  the  Sparrow  with  his  third  lid  drawn  over 
the  globe  (without  closure  of  the  paired  lid  margins)  during  som- 
nolent hours,  as  is  said  to  be  the  case  in  some  Birds  of  Prey  the 
Hen,  etc  The  soft  sausage-like  rolls  of  each  lid-edge  approach 
one  another  and  close  the  interpalpebral  space  in  a  fashion  entirely 
unlike  the  eyes  of  the  higher  vertebrates.  However,  even  when  the 
edge  of  the  third  lid  is  incompletely  drawn  over  the  globe  the  edges 
of  both  hds  make  slight  but  quite  apparent  efforts  to  close,  as  if 
here  were  slight  contractions  of  the  marginal  fibres  of  the  orbicu- 
laris. These  winking  efforts  are  more  marked  when  the  membrane 
sweeps  entirely  over  the  interpalpebral  apace;  but  in  this  consemmal 


^ylids  and  Lachiymal  Apparatus  of  Birds.  7 

contraction  of  the  true  lids  their  margins  do  not  approach  one  an- 
other,  and,  indeed,  rarely  reach  the  sclero-oorneal  junction. 

The  intcrpalpebral  line  of  closure  in  small  Birds  is  irregular  in- 
terrupted and  wavy;  nor  are  the  two  intermarginal  spaces  accurate- 
ly opposed  to  each  other,  as  in  Man.  The  Sparrow  probably  does 
not  oppose  more  than  one-half  his  lid-margin  in  the  act  of  eye- 
closure,  but  shuts  off  his  conjunctival  sac  from  the  outside  world 


»ul«rl.  muscle  flbrerit  the  iL'  Po  n.™  Slii  I?  "H"*  "■S"""*"''  O^  "■■'>'- 
of  the  Irl.;  Rp°rS-lVe  n.d  ■„?  th?  y;„..'5''"  """"^  >}">■  ™'11«1  muscle. 
8P,  .upenoV  pSipete.  ^'„,''c'i2:''T',',l'r.'uTb,'uv™rui^i.p¥.'r  nt"'  "'"■"^ 


*  ('aee)  A.   Wood. 

by  pressing  the  soft,  convoluted  marginate  rolls  into  one  another. 
The  difference  between  lid  closure  in  the  Sparrow  and  most  of  the 
higher  vertebrates  is,  roughly  speaking,  that  between  a  roller-desk 
cover  and  that  of  the  mouth  of  a  tobacco  pouch. 

The  movements  of  one  nictitating  membrane  (or  third  eyelid) 
is  in  most  birds  probably  independent  of  the  other,  although  they 
generally  act  together.  In  an  adult,  male  Sparrow,  whose  cornea 
had  been  irritated  by  manipulation,  the  average  nictitations  of 
five-minute  observations  was  55,  while  in  the  fellow  eve  the  winking 
was  reduced  to  47.  In  a  darkened  room  the  number'of  nictitations 
fell  to  41.  The  extremes  of  numerous  observations  under  various 
conditions  of  rest,  darkness,  bright  illumination,  after  the  Bird 
had  flown  about  the  room,  after  irritating  the  cornea,  etc.,  were 
(during  rest)  33,  and  (during  exposure  to  direct  sunlight)  01. 
Under  the  last  named  condition,  while"  the  nictitating  membrane 
was  drawn  over  the  globe  rapidly  and  completely,  it  was  returned 
to  place  very  slowly,  so  that  the  eye  was  covered  by  the  membrane 
during  a  relatively  longer  period  than  usual. 

In  most  Birds,  the  lids  of  the  Sparrow's  eye  close  immediately 
aft«r  or  just  before  death.  This,  as  is  well  known,  is  entirely  dif- 
ferent in  Man  and  many  other  Mammalia;  and  the  explanation  is 
that  the  lid-closer  is  really  a  smooth,  sphincter  muscle  innervated 
by  the  sympathetic,  which  continues  to  act  after  the  departure  of 
consciousness  and  after  the  eye-openers  (innervated  by  striped 
muscles)  have  ceased  to  be  under  control  of  the  will. 

The  sensory  nerve  supply  to  the  lid  is  also  entirely  different  from 
that  of  Man.  Slonaker  found  that  it  is  from  the  lachrymal  branch 
of  the  fifth  nerve  only,  which,  after  giving  off  branches  to  the 
lachrymal  gland,  divides  into  two  porUons,  one  going  forward  into 
the  lower  lid  and  uniting  with  the  superior  maxillary  nerve.  As 
yet  unverified  is  his  belief  (from  dissections  of  the  parts  involved) 
that  minute  branches  from  what  he  calls  the  frontal  nerve  may 
send  sensory  branches  to  the  conjunctiva  and  to  the  skin  about  the 
external  canthus. 

One  of  the  most  interesting  organs  of  the  avian  eye  is  the  third 
eyelid  or  nictitating  membrane,  Fumagalli  has  furnished  an  elab- 
orate description  (Intemat.  Monatschr,  f.  Anat.,  1899,  p.  1S9)  of 
the  minute  anatomy  of  this  membrane,  as  found  in  the  Hen  and 
Pigeon.  Slonaker  and  the  writer  have  not,  so  far,  entirely  investi- 
gated the  nerve  and  blood  supply  of  the  Sparrow,  but  agree  with 
Fumagalli  and  other  investigators  that  the  nictitating  membrane 


ff;/c/i'rf»  and  Lachrymal  Apparatus  of  Birds.  9 

is  composed  of  (1)  an  anterior  epithelial  layer,  (2)  a  middle  con- 
nective tissue  layer  and  (3)  a  posterior  epithelial  layer. 

The  anterior  epithelial  layer  has  the  appearance  of  typical  pave- 
ment epithelium.  The  deep  layers  are  more  cylindrical  in  form 
while  the  superficial  are  more  flattened  and  show  oval  nuclei 
Pigment  cells  begin  in  the  deep  cells  but  get  less  and  less  in  amount 
as  the  surface  is  reached. 

The  middle  layer  constitutes  the  true  substance  of  the  nictitatin.' 
membrane  and  is  largely  made  up  of  elastic  fibres  interwoven  with 
connective  tissue  fibres.  The  former  are  most  numerous  immedi- 
ately under  the  epithelial  layer.  The  middle  layer  is  provided  with 
numerous  blood-vessels,  nerves,  and  a  number  of  tubular,  solitary 
glands.  Slonaker  and  the  writer  have  not  been  able  to  find  the 
latter  in  Passer,  but  we  do  recognize  there  glands  which  are  some- 
times straight,  and  sometimes  globular,  like  sweat  glands.  Their 
openings  are  on  the  anterior  surface  of  the  membrane. 

The  posterior  epithelial  layer  is  composed  of  cylindrical  epithe- 
lium two  and  three  layers  deep.  The  deepest  cells  are  polyhedral  in 
diape,  while  the  more  superficial  have  long  prismatic  elements 
This  layer  of  the  conjunctiva  is  finally  continued  as  modified  ante- 
nor  corneal  epithelium. 

According  to  FumagalU,  the  elastir  fibres  of  the  third  lid  run  in 
all  possible  directions  through  the  connective  tissue  bundles  to 
fonn  a  thick  network,  which  may  be  resolved  into  three  layers 
Puriiennore,  a  bundle  of  these  fibres  is  shown  extending  from  the 
base  to  the  apei  of  the  lid.  It  lies  in  the  deep  portions  of  the  con- 
nective tissue,  directly  on  the  posterior  epithelial  layer.  From  this 
deep,  basement  or  foundation  layer  of  larger  fibres  there  stretch  at 
right  angles  to  it  more  delicate  fibres  through  the  whole  width  and 
thickness  of  the  membrane,  and  terminate  in  the  cells  of  the  ante- 
rior epithelial  layer. 

This  strong,  deep-lying  bundle  becomes  thicker  the  nearer  one 
approaches  the  free  border,  until  it  forms  two  or  three  fibrous 
bundles  measuring  123  microns  wide  that  eventually  becomes  part 
of  the  tendon  of  the  pyramidalis  muscle. 

Fumagalli  finds  that  posteriorly  the  elastic  connective  nerve-fibre 
bundles  are  so  disposed  as  to  form  a  subepithelial  network  from 
which  still  finer  fibrils  extend,  some  of  which  terminate  in  end- 
corpuscles. 

Slonaker  and  the  writer,  after  considerable  time  spent  in  an  in- 
vestigation of  the  subject,  conclude  that  the  nictitating  membrane 
18  a  conjunctival  duplication— a  thin,  translucent  membrane  com- 


10 


Catey  A.  Vfood. 


The  free  margin  of  a  portion  posterior  to  it  is  set  with  pigment 
posed  of  delicate  connective  tissue  interspersed  with  elastic  flbna 
running  in  various  directions.  It  has  a  firm,  thickened,  free  mar- 
gin, but  no  hyaline  cartilage  cells.  This  latter  provision  enables 
the  free  border  to  be  closely  applied  to  the  cornea,  so  that  when  it 
sweeps  over  the  latter  it  carries  with  it  some  of  the  fluid  secrotion 
of  the  Harderian  gland  and  thoroughly  cleans  and  uioistens  the 
corneal  surface.  The  presence  of  elastic  fibres  gives  to  the  third 
lid  the  qualities  of  a  thin  rubber  band ;  when  put  upon  the  stretch 
it  flies  back  instantly  the  moment  the  traction  or  "pull"  is  released. 


«,  ?"'*■  * — Enlarged  Camera  Drawings  Showing  tile  Marginai  Plait  of  tile 
Nictitating  Membrane,  Botti  Extended  and  Compressed.  (Wood  and  aion- 
aker.) 

MP.  Marginai  plait;  NE.  epltiiellum  of  tlie  nictitating  membrane:  CE. 
conjunctival  epithelium;  LE,  lid  epithelial  lining. 

cells,  but  this  marginal  pigmentation  is  much  less  marked  in  the 
Sparrow  than  in  other  birds — the  Snow  Goose  and  Ostrich,  for 
instance.  A  sectio-  .  the  third  lid  at  right  angles  to  the  free 
border  (sec  the  illustration)  shows  the  latter  to  be  triangulir  in 
shape,  like  half  an  arrow-head,  and  to  be  thrown  into  folds  both  on 
its  anterior  and  posterior  surfaces.  Interesting,  also,  are  the  basal 
folds  of  conjunctiva,  somewhat  like  the  folds  of  transmission  of 
the  human  conjunctiva,  disposed  so  as  to  allow  of  considerable  and 
rapid  excursions  of  the  membrane  back  and  forth  over  the  eyeball. 


Efelidt  and  Lachrymal  Apparatus  of  Birds.  1 1 

In  the  study  made  by  Slonaker  and  the  writer  on  the  eye  of  tho 
Sparrow  and  other  Birds  they  found  Slonaker's  marginal  plait  (see 
cut)  not  only  in  numerous  sections  of  the  Sparrow's  third  lid,  but 
in  all  the  other  Birds  so  far  examined ;  it  is  certainly  well  marked 
in  such  unrelated  species  as  the  Sooty  Tern,  the  Red-Headed  Wood- 
peclcr,  and  in  various  Pigeons.  Strange  to  say,  Fumagalli  (Ueber 
die  feinere  Anatomic  des  dritten  Augenlides,  Intertiaiional.  lion- 
atstchr.  fiir  Anatomie  und  Physiologie,  Vol.  16,  p.  189,  1899) 
makes  no  mention  of  this  important  structure,  and,  although  the 
whole  subject  is  by  him  elaborately  illustrated  by  well  executed 


Ldo 


I  the  work  of  FumasalH,  the  lower  i 


plates,  he  pictures  the  Pigeon's  accessory  eyelid  as  lacking  in  the 
marginal  plait. 

All  vertebrates  possess  at  leaut  six  extraocular,  bulbar  muscles- 
four  recti  and  two  obliques.  Birds  have  two  more  (that  control  the 
movements  of  the  third  eyelid)  viz. :  the  quadratus  muscle  and  the 
pgramidalis,  which  are  inserted  into  the  posterior  hemisphere,  bo- 
hind  the  scleral  insertion  of  the  recti  muscles. 

Confirming  the  observations  of  Kalt  (Encyclopidie  francaise 
d'Ophtalmologie,  Vol.  Ill)  and  others,  Slonaker  and  the  writer 


12 


Caseff  A.  Wood. 


found  the  quadrate  muscle  to  be  larger  aud  better  developed  than 
the  pyramidalia. 

The  muacultu  quadratua  a  inserted  into  the  sclerotic  just  behind 
the  insertion  of  the  rectus  superior  muscle.  Its  attachment  fills  in 
the  space  between  the  superior  and  internal  recti  muscles  on  the 
superior  edge  of  the  latter.  From  this  insertion  all  its  fibres  are 
directed  toward  the  optic  nerve.  The  free  extremity  of  the  quad- 
rate muscle  is  about  one-third  as  large  as  its  size  at  insertion.  Cv.u- 
sequently  it  pi'esents  a  triangle  with  a  truncated  apex  rather  than 
a  square,  as  its  namr  indicates.  At  this  point,  instead  of  having 
another  insertion,  fixed  or  mobile,  the  muscle  abruptly  ends  in  a 
tendon  which  folds  on  itself  to  form  a  fibrous  loop,  intended  for  the 
passage  of  the  pyramidalis  tendon. 


Fig.  6 — Posterior  View  of  the  Left  Eye  of  the  Sparrow  with  the  Reotuti 
Superior  (Re),  Inferior  (R  inf),  Externus  (Re),  Internus  (R  In),  and  the 
Superior  (OS)  and  Inferior  (01).  Oblique  muKles  laid  back  to  show  th« 
arrangement  of  the  Quadratus  iQ),  Pyramidalis  (P)  and  Tendon  (T)  in 
relaUon  to  the  Optlo  Nerve  (Op),  x  8.     (Wood  and  Slonaker.) 

The  pyramidal  muscle,  which  is  much  smaller,  is  inserted  under 
the  anterior  half  of  the  inferior  rectus  muscle  and  on  a  line  3  or  4 
mm.  in  front  of  the  edge  of  the  muscle.  It  then  reachep  the  ante- 
rior surface  of  tht  aptie  nerve  and  ends  in  a  tendon  which  passes 
through  the  loop  encircling  the  superior  surface  of  the  optic  nerve, 
then  enters  a  groove  in  the  sclerotic,  wht  it  is  held  by  a  contrac- 
tion of  the  capsule  of  T^on.  It  then  passes  from  within  out,  be- 
tween the  inferior  and  the  posterior  recti  muscle — ^nearer  to  the 
latter — interrupts  the  bony  circle  about  the  nerve  (in  tlie  Owl  it  is 


Eyelids  and  Lachrymal  Apparatus  of  Htrds. 


13 


attached  to  aa  spophyeiB  of  the  bony  circle)  and  readies  the  ihm- 
tcrior-inferior  angle  of  the  third  eyelid,  to  which  it  ii  joined  and 
of  which  it  formed  an  integral  part. 

At  this  point  the  (flat)  tendon  of  the  pyramidaliH  lies  in  a 
groove — almost  a  tube — on  the  eyeball.  It  now  enters  behind  the 
conjunctiva,  pierces  the  lower  sac  at  a  point  slightly  posterior  to 
the  median  plane  of  the  eye,  and  is  attached  mostly  along  the  free 
border  of  the  third  lid,  aa  a  rope  is  bound  to  a  sail.  The  fibres  of 
the  tendon  are,  some  of  them,  also  spread  out  fan-like  and  are  lost 
in  the  tissues  of  the  nictitating  membrane. 

As  the  posterior-superior  attachment  of  the  third  lid  to  the  globe 
is  posterior  to  the  vertical  plane  and  well  up  in  the  superior  cul-dts 


Fig.  7 — Posterior  View  o'.'  the  Left  Eye  of  the  Sparrow  Showing  Ar- 
rangement of  MiiBcles  and  Gl^ndB.     x  8.     (Wood  and  Slonaker.) 

L.  I«chrj-aial  gland;  h.  Harderlan  gland;  re,  rpctus  externua;  rl.  rec- 
tus Internua;  r  inf,  rectus  inferior;  rs,  rectus  superior;  oi,  obliques  Inferior; 
OS,  obliques  superior;  q,  quadratus;  t,  tendon  from  pyramidalis  muscle  to 
nictitating  membrane;  op,  optic  n^jrve. 

sac,  it  will  be  readily  seen  that  the  down-and-out  puU  of  the  tendon 
of  the  pyramidalis  must  cause  the  free  border  of  the  nictitating 
membrane  to  glide  over  the  globe  toward  the  posterior  canthus. 
In  ordinary  contractions  it  seems  to  be  drawn  over  to  the  sclera. 

Like  the  external  rectus,  the  quadrate  and  pyramidal  muscles  are 
innervated  by  the  sixth  pair. 

Generally  speaking,  the  oculomotor  apparatus  of  Birds'  eyes  is 
not  endowed  with  great  power  and  the  movements  of  the  eyeballs 
are  much  restricted.  The  protective  muscular  apparatus  is,  how- 
ever, highly  developed. 


14 


Co*'*  A.  Wood. 


l»  free  of  foreign  matter  .„dT.T*      ^  """"■'  ^  """  "  •>>»" 

«;e  Sp.rrornicti^,;-;:^^7-;'-' •  2  *« '™  '"««*■'  »' 
the  npper  cul-de-Mc     In  tw.     ,    ^      .*' ™  "*■"«' ""d  tow.rd 

befor,,  behind  ind  .t  L  ^JL  K  ™°""""'  '''""'  ™«'«J 

the  dm  figure  the  ,ligh  v  ot^en.i  """J""''"™'  ^P-"»"'""-  '» 
general  ouUine  of  th  bart  ofTflll'  'T^^"  '""'"  P"""""  'h" 
of  it.  fluke,  cut  oi  clo'^to  th,Tfr V;  "'  n  ""'■"  '""  "■"' 


ing  parts  are  interesting     It  wn..w  .„  ,.  . 

process  or  band  is  obliterated  by  then''  "'  "?"  "'"'"  '^'""•'  *» 
muscle  when  the  membr^e  i.  "  "'V^'^'""'  ™  "  »'  *e  pyramidal 
detritus  (mixed  ™Str  H  T*"  °'""' "'"»™-^''-  The  corneal 
before  the  shelfo.g™t^t„f"tret:Z'""'r.'  ^  *""  """'^^ 
or  the  sharp  mar^n  ofTli^:  inT^.V"'^  "  "■^'-  -""^^^ 

P-ivetd"  h"  Sr™  *'  "■  """"^""'  »""  ''-^™*-  =- 

tion  is  apparent     The  f,''"'.*" '- '"«on,  a  quite  different  condi- 

PParent.    The  marg,n  of  the  pectinate  fold  now  rises  and 


HyMd.  .ml  LochrymalAppaniu,  of  Bird,. 


U 


«tera.l  inrfMe  of  the  thin!  IM  rin!i   T?  u  '"  ■"•■■«'"  »»'' 

the  entrance  of  the  «h™^,  li"'  Th  "  ■      "*  '?"""''>  "'""•' 


1899  and^„*.™«<.  Vr^r  /^^  ''  (Wi><«..  Leipzig, 

iieei;ti:^Sor4°r'a:'/Vtf  ^^^  ^''^"'^'"  -^  «'«>" 
ope..  Mo.  t.  ^^:^r^zr^^f:^:^zzi 


u 


Ciury    I.  Wood. 


the  ^«ted  product  i.  ,i«id.    Thi.  gl.nd  i.  l,rg„  th.n  the  l«h. 
rymal  glwd.  .nd  belong,  to  the  tubul.r..l»eol.r  type 
According  to  S.rdemwn  (Britrig.  ,ur  Anatomi,  der  Tr«n.n 

l.«  in  the  outer  ,ngle  of  the  eye  .bout  the  e<,u.tor  of  the  glo^ 

T!,  ",'*''"' ™P""'««»'li"  "'lobular  .tructure.    In.ide  e.ch 
obule  one  find,  .collecting  .p.ce  connected  with    ubul.r  duct 

i™:f,.lt'°.  r    "'"  ""■"' " "'  ""■"■ ''''"  ^ "' 

In  the  Hen  the  f<,«,r  ,analiculu,  i,  the  ,ni.ller  of  the  two  cnal. 
cnthu..    It,  flattened  opening,  continuou,  with  the  ponp.lpebr.1 


.hf'£.c«i-c^'„-.VU"'ReSX'f  n"°<«"AF«-..  w.n.  or 


fZttatr"!  '  """■  '"'•     ^^  ""P^^  o^iculus,  separated 
from  ,te  fellow  by  a  narrow  bridge  of  tissue,  ban  an  opening  about 

jmd  .t,ll  farther  toward  ihe  front  „f  the  beak  than  the  low,:,-  „,«„. 

t.nee'of7r''"rh'"  fb"  ""'"'  """"  ""^  '''°  ™""''  ^^  '  <"-- 
tanee  of  3  mm.,  when  they  join  to  form  th,-  lachrymal  duct  whose 

»  .bre  .s^ual  to  that  of  the  combined  upper  ^d  lower  c  a.Mcut 
tZ^^^"''^^'  ^™  *""  "O  *«"-<iefined  lachrymal  sac  (as 

e^^r  la^r^  j:^::tSd:t:  =t^n:tr  ^ 
r  Jlt,^:::  ;;f  ^- — '»'«■—".  nieinS 


^H'l'iixxidUckrymatApparatutofBiriM.  \J 

Th.  couw  or  Ih,  twr.,  ,-.  ...  th.  ««reU«„  m.lnly  of  Hirder', 
g Und.  i.  qu.t,  diffe„nt  from  th.  l«h,ym.l  dr.i„.g,  "  M.„ 
Although  m.r.1  writ.™  .pel,  of  the  .vi„  l„hrym^l  fluid  .. 

»to  «..  po.,er       ..re.    th*,  .utem.,nt.  .re  mi.le«ii„,,  Tf  ^ 

number  of  .yi.n  specie.,  demoM'nte.  th.t  unleu  „ne  include  th. 

".t'V'T  h"  "",r  "'  "■'  """■""  ■•  ">  '"C  P  o  tt 
n.re.,  the  l.chrvm.l  duct  of  Bird.  ha.  little  to  do  with  the  n.« 
PM-ge.,  but  i.  .„  i«,l.ted  tub.  crried  through  and  p«t   he  nZ 

^l!r,h?»       ^^      "?'  "  ""^  """y-  "  '•  -"»  known,  i.  , 


M,  maxlllKry  alnuB;  T.  turblnala  '   *  ""*'*  *'■■  '>•«'»  cut  away; 

tte  ;u^o  ll  °^"'^  ™  "^  "'^'  P^"''"  ^^o-'  lading  to 

^ttl     „      T'"f '   '"''™"-^   '"*™'^'"^   "   '««^«'»'y   drainage 
t^ZlZT^l  '"'''""  ""  "-^^"^  '"^  -chn^ai^retiol 
The  orifices  of  the  c.nalicnii,  upper  and  lower,  are,  as  stated 
no^  placed  on  to  lid  margins  at  the  anterior  canthis,  b^t  "neraU; 

Mmute  shallow  grooves,  b.      ■       .wn  in  fte  Hen,  lead  from  the 
canthns  around  and  close  to  u.e  margin,  of  both  lids  and  " 


» 


C—f  A.  Wood. 


gnttai^llka  cooduit  iot  the  purpoM  o(  convejring  tha  lichrym*! 
fluid  in  tha  dinction  o(  tha  pnih.'te.  Tkaaa  opaningi  *ra  ralitivaljr 
luja  ud  alnyi  commnDinta  with  aomapondinglj  luft  oumlienll, 
whidi  in  Uw  Sparrow  ara  about  11  mm.  long.  Thay  Join  tu  (orm  • 
laiga  fibroua  tuba,  linad  with  apithalinm,  tba  lachrymal  duct,  that 
runa  diractly  downward  and  forward  toward  tha  madian  Una  until 
it  opani  into  the  choanal  ilit,  tha  marginata  ipinea  of  which  diiact 
ita  contcnti  backward  into  tha  aaophagaal  opening. 

In  tha  Sparrrw  a  probe  1  mm.  in  diameter  can  readily  be  paaaed 
through  the  lachrymal  duct  and  thii  probably  reprcaenta  the  lumen 
of  the  tube.  The  canaliculi  are  about  1  mm.  long,  while  the  length 
of  the  common  duct  may  be  let  down  aa  3.6  mm. 

Slonakar  and  the  writer  have  not  Ik  n  able  to  demonatrata  the 
prcaence  of  ciliated  epithelium  in  the  duct  mucoca. 

The  opaninga  analogiua  to  the  human  puncla  are  irregularly 
rouuded;  tba  upper  one  being  diitinctly  larger  and  uore  patent 
than  the  lower.  Correaponding  to  theae,  Slonaker*!  ptripalpehral 
groove  ia  deeper,  longer  and  better  marked  at  the  conjunctival  r  '■ 
gin  of  the  upper  lid  than  at  the  correaponding  border  of  the  lower 
lid. 

The  principal  facta  to  be  remembered  about  the  lar°  i  drain- 

age in  Birda  ara  ( 1 )  that  tha  free  margin  of  tha  third  ,  anchor> 
or  balf-epear-ahaped ;  (2)  the  free  edge  probably  pn  «  before 
it — icraper-like — the  Harderian  fluid,  thui  cleansing  ,  i  cornea 
on  the  contraction  of  the  pyramidalia  and  qkjdratua  muacies;  (3) 
at  the  instant  of  reat  ihia  same  secretion,  supplemented  or  not  by 
the  lachrymal  fluid,  is  pulled  (bucket-like)  back  and  emptied  into 
the  canaliculi;  (4)  during  thr  erformtuice  of  this  act  it  ia  to  be 
remembered  that  at  he  end  ol  '■'sa  the  most  complete  excursions 
of  the  nictitating  membrane  the  lower  edge  of  the  lower  lid  ad- 
vances only  about  half  a  millimetre,  whiU,  although  there  is  a 
aimultaneoui  twitching  of  ita  palpebral  margin,  the  upper  lid  ap- 
parently does  not  come  forward  at  all. 


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